Field of the Invention
This invention generally relates to electroplating metal layers onto substrates. More specifically, it relates to apparatus for controlling the composition, flow, and potential distribution of electrolyte while electroplating a wafer.
Related Technology
In electronics, a wafer (also called a slice or substrate) is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices. The wafer serves as the substrate for microelectronic devices built in and over the wafer. The fabrication process of microelectronic devices involves many steps including, e.g., doping, electroplating, etching, and photolithographic patterning.
Electroplating uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. This form of electroplating is widely used to deposit conductive metal on semiconductor wafer in the manufacture of microdevices. Electroplating can also oxidize anions onto a solid substrate, as in the formation of silver chloride on silver wire to make silver/silver-chloride electrodes.
In electroplating of metal cations onto a wafer, the wafer forms the cathode of the circuit. One form of electroplating involves an active anode (also known as a consumable anode), wherein the anode is made of the metal to be plated on the wafer. Both the anode and the wafer are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply provides a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the electrolyte. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the wafer cathode, such that they “plate out” onto the wafer. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated. In this manner, reactions are balanced, and ions in the electrolyte bath are continuously replenished by the anode.
Other electroplating processes may use a non-reactive anode (also known as a non-consumable or dimensionally stable anode) comprising, e.g., lead or carbon. In these techniques, the anode does not provide cations for the plating. Instead, ions of the metal to be plated must be periodically replenished in the electrolyte as they are drawn out of the solution. The reactions in a non-consumable system are unbalanced. The two reactions are:H2O→½O2+2H++2e− (anode)Cu+2+2e−→Cu (cathode).
Needs exist for methods and apparatus for improving electroplating efficiency and quality by controlling the composition, flow, and potential distribution of electrolyte.